Ulcerative Lymphangitis (Big Leg)

Ulcerative Lymphangitis (Big Leg) is characterized by the development of cutaneous form of pyogranulomatous abscess in subcutis, mastitis, internal abscessation, a necrotic and ulcerative dermatitis on the heel of the foot.

Ulcerative Lymphangitis (Big Leg) lesions are restricted to limbs. Edema and lameness of the affected limb noticed.

Etiology

• The disease is caused by Corynebacterium pseudotuberculosis biotype-2.
• It is a saprophytic and intracellular organism.
• Biotypes causing ulcerative lymphangitis in cattle and horses are not the same biotype that causing caseous lymphadenitis in sheep and goats.
• They are gram positive and catalase positive, non-spore forming, non-motile, rod-shaped bacteria that are straight or slightly curved.
• The bacteria group together in a characteristic way, which has been described as the form of a “V”, “palisades”, or “Chinese letters”.
• They may also appear elliptical.
• They are aerobic or facultative anaerobic, chemo-organotrophs, with a 51–65% genomic G:C content.
• They are pleomorphic through out their life cycle.
• They come in various lengths and frequently have thickenings at either end, depending on the surrounding conditions.
• Their size falls between 2-6 micrometers in length and 0.5 micrometers in diameter.

Epidemiology

Prevelence of infection

• The disease affects the ability of the horses. It is the most important disease of North Africa, Israel and Asia.
• Generally, the morbidity rate is 5% but during epidemic period the morbidity recorded was found as 5-35% and culling mortality rate is 16%.

Economic impact

• The loss usually associated with a increased culling rates, a decrease in milk production and changes in quality of the bulk tank milk due to increase in somatic cell count.

Predispoing factors

• Unhygienic and wet conditions predispose animals to infection, particularly of the lower legs and ventral region.

Sources of infection

Arthropod vectors such as Habronema spp larva and stable flies and contact with fomites such as contaminated soil and grooming equipment.

Transmission

• Sporadic form of Cutaneous ulcerative lymphangitis and outbreak form occurs during the summer months of the year and is correlated to the prevalence of house flies.
• The bacteria probably enter via skin wounds including IM injections, arthropod vectors such as Habronema spp larva and stable flies, and contact with fomites such as contaminated soil and grooming equipment Nevertheless, highest incidence occurs during winter season.
• The entry of the organism occurs through insect bite wounds. Also, contact with a infected herd, mechanical or passive spread of infection occurs by Diptera species.
• The disease can also spread through breach in the skin of limb, inanimate objects.

Host affected

• Cattle, sheep, goats and horses are susceptible.

Pathogenesis

• It is a saprophyte, intracellular organism, spread through abrasions and set up the disease.
• The cytotoxic surface lipid coat of the organism helps the intracellular survival, invasion of the organism in to lymphatic vessels which results in the formation of abscess.
• The phospholipase exotoxin produced by the organism increases the vascular permeability and inhibitory effects of phagocytes and thereby spread the infection in the host.
• Ulcerative lymphangitis, and skin abscessation occurs in mature animals and necrotic, ulcerative dermatitis in heel of foot occurs in heifers.

Clinical Signs

Horses

• In the beginning, wound infection, swelling, pain on the pastern region, severe lameness, nodules in the subcutaneous tissue, specially around the fetlock and all parts of the body develop.
• Nodules enlarge to 5-7 cm diameter, rupture and discharges a creamy green pus.
• The ulcerous lesion has ragged edges, and a necrotic base.
• Abscess develop in lymphatic vessels and drain into lymphatics which become enlarged, hard, and may lead to secondary ulcers.
• Healing may take place in a week or two but new abscess leads to persistence of disease for up to one year.

Cattle

• The symptoms and lesions are similar as in horses.
• Enlargement of draining lymphnodes and discharge of gelatinous clear exudate from ulcers seen.
• Cutaneous form Single or multiple painful abscess of 15-20 cm in diameter on the skin, subcutaneous tissues of head, flanks, shoulders, neck, hind legs, stifle joints with a fine fibrous tissue capsule develop.
• Abscess rupture, drain out serosanguineous exudates or blood stained yellow pus.
• Lymphnode are enlarged without generalized lymphangitis.
• Only lesser percentage of animals are re-infected after recovery from infection.
• In necrotic and ulcerative dermatitis, a prominent lameness in the distal parts of the foot is observed.

Zoonosis

• Ulcerative Lymphangitis (Big Leg) develops a public health importance when personals having close contact with infected animals while consuming non-pasteurised infected milk.

Necropsy Findings

• The onset of ulcerative lymphangitis in horses is slow and usually manifests by painful inflammation, nodules, and ulcers, especially in the region of the fetlock; occasionally, the edematous swelling can extend up the entire limb.
• The exudate is odorless, thick, greenish white, and blood tinged. Usually, only one leg is involved.
• Lesions and swelling progress slowly, and the condition can become chronic with relapses.

Diagnosis

• Based on the clinical signs and necropsy findings. Isolation and identification of the organism from infected tissues and discharging pus.
• No serological tests are available for screening infection in cattle or horses. But the tests meant for caseous lymphadenitis in sheep can be used for diagnosis of ulcerative lymphangitis,

Sample collection

• Samples for culture include aspirates of abscesses, swabs of purulent exudate beneath crusts associated with folliculitis, and punch biopsies.

Differential diagnosis

• Epizootic Lymphangitis
• Glanders
• Sporotrichosis
• Rhodococcosis
• Streptococcosis
• Staphylococcosis
• Pseudomonosis
• Ermatophytosis
• Equine Cryptococcosis
• North American blastomycosis
• Onchocerciasis

Treatment

• The organism is sensitive to all common antibiotics and drugs excluding aminoglycoside group of drugs.
• Treatment of infected animals does not affects the recovery period from infection.
• Parenteral injection of penicillin or tetracycline can be used.
• Early stages of infection can be treated with autogenous bacterin.
• Lymphangitis and early abscess swellings are treated with hot packs, poultices, or hydrotherapy.
• Abscesses are lanced and flushed with iodine solution.
• Large abscesses require surgery.
• Skin lesions and grossly contaminated limbs are scrubbed daily with an iodophor shampoo.
• Penicillin or trimethoprim-sulfa combinations have been given; however, antimicrobial treatment may prolong the disease by delaying abscess maturation.
• Phenylbutazone relieves pain and swelling.
• General supportive and nursing care is indicated. If treatment is successful, the swelling gradually recedes over days or weeks.

Prevention

• An experimental bacterin-toxoid was not effective in field trials.

Control

• Cleaning of wound with specific antiseptic and antibiotic solution and disinfection of stable and infected foots is essential.
• Insecticide spraid on to the head and abdomen.
• Care should be taken to avoid synthetic pyrethroid residues.